Oil well spacer fluids

ABSTRACT

A high stability, nondamaging spacer fluid is provided containing readily available weighting agents such as calcium carbonate and iron carbonate dispersed in water using a polymer viscosifier, a salt inhibitor, a primary sulfonated dispersant and a secondary fatty acid amide dispersion. Conventional high density weighting agents can also be used. The spacer fluid is stable over a temperature range of about 32°-300° F for extended periods with densities ranging from 11 to 17.6 pounds per gallon.

Fluids that were previously used as completion fluids, ballast fluids or packer fluids were expensive or were not stable at elevated temperatures. They would thin or decrease in viscosity and gel strength with time and/or temperature to permit settling of solids. They had insufficient fluid loss control, could only be weighted to about 13.6 pounds per gallon (ppg) without using a formation damaging material, were too corrosive or had a tendency to solidify. Typical applications are described in U.S. Pat. Nos. 2,805,722; 3,254,714 and 3,378,070.

The high stability fluid of this invention, referred to herein as "HYDROWATE," is a water base fluid for use as a ballast, spacer, packer, workover, completion, drilling or perforation fluid, or in conjunction with gravel packing. Its design is such that many of the undesirable properties of previously used fluids have been eliminated. It is composed of water (i.e., fresh or brines), dispersants (optional in some cases), a polymer or viscosifier, a weighting agent such as calcium carbonate and/or iron carbonate (which are acid soluble materials) for weight or density, and an inhibitor such as potassium chloride, 3% by weight of water, for inhibition to prevent damage from the filtrate to water sensitive formations.

The high stability fluid of this invention can be used over a broad temperature range from freezing temperatures up to about 300° F. under appropriate pressure for extended periods. It can be used as ballast to furnish a total weight, as a weighting fluid to supply a minimum or preselected hydrostatic head with a density of about 11 to 17.6 pounds per gallon (ppg) or as a relatively inert, relatively incompressible spacer fluid to separate or move other fluids or maintain pressures on surfaces or formations under either static or dynamic conditions either during chemical or mechanical operations such as drilling or between operations.

The slurry weight of HYDROWATE can be increased to 16 ppg using calcium carbonate weighting agent as shown in Table 1 and to 17.6 ppg using a combination of calcium carbonate and iron carbonate weighting agent; these materials are acid soluble. Viscosity, yield point, and gel strength can be controlled within limits by either varying the amount and type of dispersant used or by varying the amount of viscosifier (as shown in Tables 4 and 5). The viscosifier, along with the weighting materials, impart good fluid loss control and provide sufficient gel strength to keep the weighting materials suspended under static conditions at temperatures up to 290° F. After remaining static at 250° F. for 60 days, there is no settling of particles in the HYDROWATE at densities or weights of 12 and 16 ppg. Also, no settling of particles occurs in a 17.0 ppg HYDROWATE after remaining static at 290° F. for 60 days. Each of these fluids can be pumped or agitated very easily, with no tendency to solidify.

Viscosity and yield point are reduced by temperature increase but not to the point of permitting settling. This reduction in viscosity should facilitate placement, and the yield point reduction will make displacement easier to achieve. Tables 1, 2 and 3 show the recipes of typical slurries from 11 to 17.6 ppg and the fluid properties of these slurries at 72°, 150° and 160° F.

Gas entrainment, as a result of reacting acid with HYDROWATE or bubbling nitrogen through the fluid, is not a problem according to laboratory test results. The gas resulting from the reaction of hydrochloric acid and calcium carbonate dissipate readily out of the fluid. Nitrogen was bubbled through HYDROWATE until it was gas cut 7%, i.e. had a 7% increase in volume or decrease in density. The addition of a defoamer to de-gas the fluid readily and continued bubbling of gas through treated fluid does not result in gas re-entrainment. A vacuum degasser is also effective in removing entrained gas or air.

Since all solids used in the preparation of HYDROWATE are substantially acid soluble, the solids can be removed readily should they penetrate the formation. The use of potassium chloride in the fluid for inhibition and low fluid loss should keep formation damage to a minimum. Flow tests through a sandstone core showed no reduction in the backflow of crude oil after HYDROWATE had been against the core face under pressure at 100 psi and 150° F. When the core was flushed with 15% hydrochloric acid following the exposure to HYDROWATE, an increase in flow rate of the crude oil was observed as shown in Table 7.

To determine the compatibility of HYDROWATE with other fluids, it was mixed with various fluids and the VG Meter readings taken of mixtures. The VG Meter is described in U.S. Pat. Nos. 2,703,006; 3,057,421; 3,327,825 and 3,435,666. The tests were run according to API Method 10B. The viscosity of HYDROWATE was reduced in each case when diluted up to 50% by volume with a bentonite mud slurry, a neat cement slurry and a gelled aqueous fluid. The results are shown in the following table.

    __________________________________________________________________________                                 Gelled                                             Contaminant                                                                              Mud      Cement   Aqueous Fluid                                      Percent                                                                               0  20 30 50 20 30 50 20  30 50                                          __________________________________________________________________________     100 rpm                                                                        Reading                                                                               275                                                                               158                                                                               92 153                                                                               108                                                                               73 50 157 137                                                                               127                                         __________________________________________________________________________

Due to the presence of a viscosifier which is used for dispersing the weighting agents and reducing fluid loss, the pressure losses or flowing frictional pressures of HYDROWATE are higher than for non-solids fluids. Reasonable rates of flow for placement and displacement, however, can be achieved. Flow rate and frictional pressure losses can be readily determined on HYDROWATE for specific conditions in view of this disclosure.

A preferred class of viscosifiers for the high stability fluid of this invention is the water soluble polysaccharides and especially the substituted nonionic cellulose polymers, such as hydroxy alkyl cellulose or cellulose ethers in which the hydroxy alkyl groups have 2-3 carbon atoms. Other substituents can be present or used which produce a water soluble cellulose which does not adversely react in the high density fluid system. The substituted cellulose should be hydratable in the high density fluid. The preferred cellulose class can be represented as a series of anhydroglucose units shown as follows: ##STR1##

The portion in brackets is two anhydroglucose units, each having three reactive hydroxyl groups. N is an integer which would give the desired polymer molecule length and preferably an aqueous viscosity of about 105-130 viscosity units of consistency at 72° F. (approximately equal to centipoise [cp]) on a V.G. Meter at 300 RPM with a 2.5% aqueous solution in fresh water.

When the cellulose polymer is treated with sodium hydroxide and reacted with ethylene oxide, an ether substituted cellulose such as hydroxyethyl ether or hydroxyethylcellulose is produced shown as follows: ##STR2##

The hydroxyethylcellulose or HEC shown has three of the six hydroxyl groups substituted by ethylene oxide; therefore the degree of substitution (or D.S.) is 3 of 6 or 1.5 per anhydroglucose unit. The preferred D.S. for cellulose polymer viscosifiers of this invention is about 1.0-3.0.

The above formula also shows that two of the substituted hydroxyl groups have two moles of ethylene oxide and one has one mole of ethylene oxide; therefore, the ratio of moles of ethylene oxide to anhydroglucose unit (or M.S.) ratio is 5 moles for two units or 2.5. The preferred M.S. ratio for HEC polymer viscosifiers of this invention is 1.5-3.0.

Thus, the preferred class of cellulose ether polymers can have various polymer lengths, degrees of substitution and lengths of side chains. Since these factors are interrelated the preferred polymers can be readily defined by viscosity in aqueous solutions. Brookfield viscosity in centipoises of preferred types of HEC are given in Table 10.

The viscosity measurement and sample preparation must be carefully controlled. The viscosity measurement must be standardized because the viscosity reading is dependent upon rate of shear, temperature, amount of agitation prior to measurement and elapsed time between agitation and measurement. The sample must be completely dissolved and a moisture correction included. Samples are dried by heating in a correction oven at a constant temperature of about 105° ± 0.5° C. for 3 hours. The samples are cooled in a desiccator and weighed at ambient temperature. The heating for about 45 minutes and cooling are repeated until repeated weights are within about 5 milligrams per each 5 grams of sample. The amount of moisture in the samples is used to calculate solution concentration of remaining portions of the cellulose polymer. The polymer solution and samples for moisture determination should be prepared at the same time to insure correspondence between the moisture correction and samples used for solution preparation. An estimated amount of polymer to prepare the desired concentration and amount of polymer solution should be weighed and stored in a moisture tight container. After the moisture correction factor is applied and the exact amount of water required is determined, the water and polymer should be carefully mixed with slow agitation. After the polymer appears to be completely dissolved, the solution should be vigorously agitated for 10-15 minutes. For viscosity measurement the solution should be at a constant temperature of 25° ± 0.5° C. for at least 30 minutes but the viscosity must be measured within two hours of the vigorous agitation, or the solution should be vigorously re-agitated for ten minutes and held at a constant 25° C. for 30 minutes before measurement.

Dispersants used for compositions of this invention are of two principal types. Either or both types of dispersants can be used over the full density range, but the primary dispersant which is referred to as sulfonate dispersant is preferably used for density up to about 16 pounds per gallon. For higher density fluids where more than one type of weighting agent and/or high loading of weighting agent is used, the secondary dispersant which is referred to as oleyl amide dispersant is used. Generally, less than about 0.4% by weight (i.e., 2.5 pounds per 42-gallon barrel [ppg]) of primary dispersant and less than about 0.45% by weight or 3 ppb of secondary dispersant is used in the high stability fluid of this invention. For low densities (e.g., 12 ppg) and under certain conditions the dispersant can be considered optional, but generally it is used for easier mixing and to improve suspension characteristics of the aqueous base fluid which may be water or brine. The maximum concentration of dispersant is usually determined by economics and the density desired, but is preferably less than about 1.5% by weight of resulting fluid.

The preferred class of primary dispersants is the product of a low molecular weight aldehyde and a naphthalene sulfonate salt. A preferred sulfonate dispersant combined with polyvinylpyrrolidone (i.e., PVP) is described in U.S. Pat. No. 3,359,225 which is incorporated herein by reference. Up to 10% PVP can be used with the naphthalene sulfonate and can be in the form of an alkali or alkaline metal salt, but preferably is a sodium or potassium salt. Other conventional dispersants such as lignosulfonates, sulfonated lignites, gluconic acid, delta lactone and lignin liquor can be used alone in some cases and in combination with a primary sulfonate dispersant.

A preferred class of secondary dispersants are fatty acid amides produced by the reaction of saturated or unsaturated fatty acid halides having about 14-18 carbon atoms per molecule with a low molecular weight amino sulfonic acid having about 1-6 carbon atoms. The sulfonic acid can have alkyl and/or aryl radicals having 1-6 carbon atoms and one or more sulfonic acid groups or salts thereof. A preferred amide is the reaction product of oleyl chloride and a C₃ sulfonic acid or sodium salt, N-methyl taurate. This preferred oleyl amide is also mixed with approximately 25-75% by weight, but preferably equal amounts, of lignin liquor. This lignin liquor is a waste product of the sulfite process or the Kraft process used in the wood pulping industry. This lignin is sulfonated with a sulfur content of preferably about 1-3% by weight. Other fatty acids which can be used are linoleic, linolenic, stearic, palmitic, myristic, myristoleic and mixtures of fatty acids. The amide dispersant can be used as a liquid or adsorbed on a relatively inert particulate carrier such as diatomaceous earth.

The water or aqueous base used to prepare the high stability fluid of this invention can be fresh water or brine containing one or more salts up to saturation. As shown herein, fresh water is preferred as the base material because it is easier to mix the ingredients if a particular order is used. A salt or inhibitor is usually added as the last component where possible. The salt serves to inhibit clays which may be encountered. The polymer viscosifier also acts as an inhibitor. Alkali metals, alkaline earth metals and ammonium salts are preferred cations of the salt, especially sodium, magnesium, potassium, and/or calcium halides such as chlorides, bromides or combinations thereof. The salt concentration should be about 0.5-15% by weight, and preferably about 1-6% by weight.

The weighting agents used for compositions of this invention are relatively inert finely divided particulate materials having a particle size with at least 80% by weight between about 2-50 microns (μ). Preferably, all or at least 90% of the material will pass through a 200-mesh U.S. Standard Sieve Screen. The particulate weighting agent should also have a specific gravity of at least 2.4 and preferably about 2.5-3.8. A preferred class of weighting agents are considered acid soluble in aqueous acids such as acetic, hydrochloric, nitric, sulfurous, sulfuric and phosphoric. This class includes calcium carbonate, iron carbonate and the iron oxides. Higher specific gravity weighting agents having a specific gravity of 4.0-7.0 such as barium sulfate and lead sulfite can be used in combination with the acid soluble weighting agents. The acid soluble weighting agents preferably have a particle size distribution so that at least 80% is between 2-20 microns in size with a mean size of about 4-10 microns. The high specific gravity weighting agents preferably have a particle size distribution so that at least 80% is between 2-50 microns with a mean size of about 15-20 microns. High concentrations of very small particles tend to increase viscosity of the resulting composition while larger particles tend to settle faster. The higher specific gravity weighting agents are not considered acid soluble for condition of use but since the high stability fluid of this invention does not invade most formations, it is considered nondamaging even with the higher specific gravity materials. The particular weighting agents and particle size distribution affect fluid loss. The viscosity and API fluid loss are determined by standard API methods such as described by API Method 10B using a direct reading rotational viscometer often referred to a VG Meter or Fann VG Meter and described in U.S. Pat. Nos. 2,703,006; 3,327,825; 3,435,666 and 3,057,421. Using the VG Meter, the viscosity of the high stability fluid of this invention should have a minimum value of at least about 49 viscosity units at 72° F. for 16 pounds per gallon density fluid. The maximum viscosity can be above 300 units for high weight fluids, depending upon limitations of the agitation and pumping equipment being used. The viscosity reading of the VG Meter is reported in viscosity units or units of consistency which approximately correspond to centipoises (cp) but is not an exact relationship since the fluids are non-Newtonian in character. The fluids can be readily weighted up to 16 ppg with one or more of the acid soluble weighting agents such calcium carbonate to form a high stability nondamaging fluid. Densities of up to about 17.6 ppg can be obtained by using agents in combination such as calcium carbonate and iron carbonate. These densities easily exceed the limitation of previously known systems which was about 13.6 ppg. Low density high stability fluids can be obtained by using low density particulate materials, in which case the amount of viscosifier may be reduced. Higher densities are obtained by increasing the amount of higher density particulate materials. The dispersants and weighting materials are preferably combined stepwise in order of increasing densities and dispersing power. For most applications, the fluid loss of the high stability fluid should be 8.0 or less and preferably less than about 5 milliliters per 30 minutes at 72° F. The preferred concentrations of acid soluble weighting agents is about 32-78% by weight of fluid or 150-512 ppb. The preferred concentrations of high density weighting agents is less than 30-65% by weight or 140-425 ppb.

EXAMPLES

Procedures for preparing the high density, high stability, nondamaging aqueous HYDROWATE fluid of this invention with properties of numerous samples are given herein. These examples, procedures and data will enable one skilled in the art to practice the invention with many obvious variations. Fluids can be prepared and modified in view of this disclosure. Tables 1-9 illustrate the ranges and concentrations of various components. Parts, percentages, and proportions are by weight unless indicated otherwise. The abbreviations ppg and ppb refer to pounds per gallon of fluid and pounds per 42-gallon barrel of fluid. All references cited herein are incorporated herein to any extent necessary.

SAMPLE PREPARATION PROCEDURE

Samples for the data in the tables set forth herein were prepared by mixing with moderate to vigorous agitation in a blender and adding ingredients slowly and uniformly in the order given as follows:

1. The required amount of tap water was placed in the blender at ambient condition;

2. With moderate agitation the required amount of sulfonate or primary dispersant was blended into the water and agitated for an additional minute;

3. With moderate agitation calcium carbonate weighting agent or primary weighting agent was blended into the water with additional mixing for two minutes;

4. With moderate to vigorous agitation HEC (hydroxyethylcellulose) viscosifier was blended into the water or aqueous slurry with additional agitation for ten minutes; secondary dispersant such as oleyl amide dispersant and secondary weighting agent such as iron carbonate or tertiary weighting agent such as galena or barium sulfate would be added at this point for densities above about 16.0 ppg; and

5. While mixing, inhibitor salt such as potassium chloride, sodium chloride or calcium chloride is added. Agitation is continued for about three minutes.

Samples are tested according to API Methods such as 10B. Viscosity measurements are taken from a direct reading viscometer such as a Model 35 Fann VG Meter using a No. 2 spring and the values indicated on the meter are doubled and recorded in the tables. Fluid loss and other values are measured by standard methods. The apparent viscosity is in units of consistency or approximately equal to centipoises and is calculated as one half of the reading at 600 RPM. Plastic viscosity is calculated as the difference between the 600 RPM and 300 RPM readings. Plastic viscosity is an indicator of the solids content of the fluid. Yield point is calculated as the difference between twice the 300 RPM reading and the 600 RPM reading. It is an indicator of the attraction between particles in the fluid in pounds per 100 square feet.

MIXING INSTRUCTIONS

For convenience and ease of preparation, HYDROWATE is preferably mixed at a location having good measuring and mixing facilities and then delivered to any remote location for use such as a well site. Storage tanks should be clean and, although settling of weight material is not anticipated during storage, should include some means of periodic agitation. The storage and mixing system should be thoroughly cleaned and inspected before and after storing the weighting agent such as calcium carbonate. Any air used for mixing or conveying should be dry.

HYDROWATE fluid is preferably mixed in a turbine blender, but can be mixed successfully using a jet mixer or ribbon blender. Typical mixing equipment is shown in U.S. Pat. Nos. 2,884,230; 3,237,805; 3,251,583; 3,463,460; 3,512,841; 3,563,517; and 3,844,351.

When using a ribbon blender, sufficient agitation to "pull" the viscosifier into the fluid is necessary or it will water wet, forming balls of polymer that will not easily disperse.

The order of addition for weights through 16.0 ppg is as follows: water, sulfonate dispersant, weighting agent, viscosifier and inhibitor, such as potassium chloride. The order of addition for weights from 16.0 through 17.6 ppg are as follows: water, sulfonate dispersant, weighting agent, oleyl amide dispersant, high density weighting agent such as iron carbonate, viscosifier and inhibitor. The oleyl amide dispersant and iron carbonate can be added together to minimize foaming or a defoaming additive can be used.

PREPARATION METHOD I USING A TURBINE BLENDER

1. Measure the required amount of water into one side of the tubine blender.

2. Continue mixing and add the required amount of sulfonate dispersant.

3. Continue mixing and add the required amount of weighting material.

4. Continue mixing and add together any additionally required amount of oleyl amide dispersant for the required density and additionally high density weighting agent such as iron carbonate.

5. Continue mixing and circulating and add the required amount of viscosifier through the hopper.

6. Continue mixing and add the required amount of inhibitor such as potassium chloride at about 10.5 ppb.

7. Continue the slurry movement and blending until desired properties are reached.

PREPARATION METHOD II USING A JET MIXER

1. Measure the required amount of water in a clean vessel.

2. While circulating, add the required amount of sulfonate dispersant.

3. Continue circulating and slowly add the required amount of weighting material such as calcium carbonate.

4. Continue circulation and slowly add the required amount of viscosifier.

5. Continue circulation and add inhibitor such as potassium chloride.

6. Continue the slurry agitation until desired properties are reached.

7. Oleyl amide dispersant can be added if lower viscosity is desired.

PREPARATION METHOD III USING A RIBBON BLENDER

1. Measure amount of water required into a clean ribbon blender vessel.

2. Add sufficient acid such as 15% hydrochloric acid to lower the pH to 6.0-6.2*. This requires approximately 0.3 to 0.8 gallons per barrel depending on the weight to be mixed.

3. While agitating the fluid, add the necessary amount of sulfonate dispersant.

4. Continue agitation and slowly add the required amount of weighting material, e.g. calcium carbonate. p 5. Continue agitation and slowly add the correct amount of viscosifier.

6. Continue agitation and add inhibitor such as potassium chloride at about 10.5 ppb.

7. Continue agitation and add sufficient 20% caustic solution (preferably NaOH or KOH) to raise the pH to about 7.5-11.5 or back to normal.** This requires approximately 0.10 gallons per barrel, depending on the density to be mixed.

Should the viscosity be less than that desired or should more stability, fluid loss control, etc., be needed to adapt the HYDROWATE for a packer fluid, the pH can again be lowered in order that more viscosifier may be added more easily. The adjustment of the pH to normal again will result in the hydration of the viscosifier to produce the desired viscosity increase. No difference in HYDROWATE properties resulted when the pH was raised to 7.5 and to 11.5 showing that the final pH is not critical as long as it is above about 7.5.

Should weight adjustment be desired, the necessary amounts of water or weighting agent can be readily determined in view of this disclosure.

                                      TABLE 1                                      __________________________________________________________________________                    Weight, Pounds Per Gallon (ppg)                                                11.0                                                                               11.5                                                                               12.0                                                                               12.5                                                                               13.0                                                                               13.5                                                                               14.0                                                                               14.5                                                                               15.0                                                                               15.5*                                                                              16.0*                                                                              16.0**              __________________________________________________________________________     Fresh Water (gal)                                                                             34.1                                                                               32.5                                                                               31.1                                                                               29.6                                                                               28.1                                                                               26.6                                                                               25.2                                                                               23.8                                                                               22.2                                                                               20.8                                                                               19.2                                                                               19.2                Sulfonate Dispersant (ppb)                                                                    0   0   0   0.2 0.2 0.5 0.5 2.0 2.0 2.5 2.5 2.5                 Weighting Agent, CaCO.sub.3                                                                   178 212 245 278 312 345 378 412 445 478 512 512                 (ppb)                                                                          Viscosifier, HEC (ppb)                                                                        7   6.5 5   5   4   3.5 3   1.5 1.25                                                                               1.0 0.5 0.5                 Inhibitor, KCl (ppb)                                                                          10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                               Initial Rheology at 72° F                                Apparent Viscosity                                                                            212 230 157 211 186 180 200 120 176 164  300+                                                                              113                 600 Reading    424 460 314 422 372 360 400 240 352 328 600+                                                                               226                 300 Reading    272 292 192 260 230 216 234 134 200 174 430 118                 Plastic Viscosity                                                                             152 168 122 162 142 144 166 106 152 154 --  108                 Yield Point    120 124 70  98  88  72  68  28  48  20  --  10                  200 Reading    208 224 143 192 170 156 172 96  144 120 396 80                  100 Reading    126 134 86  112 100 90  100 54  82  70  170 46                  6 Reading      14  16  12  12  12  10  14  10  16  24  40  18                  3 Reading      8   10  8   8   8   7   10  8   14  22  30  16                  Gel Strength (10 sec)                                                                         10  10  8   10  10  8   16  12  22  32  34  24                  Gel Strength (10 min)                                                                         12  10  12  14  16  20  30  22  42  42  52  34                  pH             8.45                                                                               8.20                                                                               8.25                                                                               8.20                                                                               8.10                                                                               8.20                                                                               8.25                                                                               8.1 8.1 8.1 8.1 8.1                 API Fluid Loss                                                                 (mls/30 min)   4.3 4.0 5.4 4.4 4.7 5.5 5.2 3.8 5.7 5.3 7.4 5.1                 __________________________________________________________________________      *0.5 pounds per barrel oleyl amide dispersant referred to as SPACER            SPERSE.                                                                        **1.0 pounds per barrel SPACER SPERSE.                                         Note: ppb - pounds per 42 gallon barrel.                                 

                                      TABLE 2                                      __________________________________________________________________________                    Weight, Pounds Per Gallon                                                      11.0                                                                               11.5                                                                               12.0                                                                               12.5                                                                               13.0                                                                               13.5                                                                               14.0                                                                               14.5                                                                               15.0                                                                               15.5*                                                                              16.0*                                                                              16.0**              __________________________________________________________________________     Fresh Water (gal)                                                                             34.1                                                                               32.5                                                                               31.1                                                                               29.6                                                                               28.1                                                                               26.6                                                                               25.2                                                                               23.8                                                                               22.2                                                                               20.8                                                                               19.2                                                                               19.2                Sulfonate Dispersant (ppb)                                                                    0   0   0   0.2 0.2 0.5 0.5 2.0 2.0 2.5 2.5 2.5                 Weighting Agent, CaCO.sub.3                                                                   178 212 245 278 312 345 378 412 445 478 512 512                 (ppb)                                                                          Viscosifier, HEC (ppb)                                                                        7   6.5 5   5   4   3.5 3   1.5 1.25                                                                               1.0 0.5 0.5                 Inhibitor, KCl (ppb)                                                                          10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                               Initial Rheology at 160° F                               Apparent Viscosity                                                                            78  80  61  71  69  60  66  104 57  63  110 49                  600 Reading    156 160 122 142 138 120 132 208 114 126 220 98                  300 Reading    92  92  72  80  80  70  78  116 66  74  120 54                  Plastic Viscosity                                                                             64  68  50  62  58  50  54  92  48  52  100 44                  Yield Point    28  24  22  18  22  20  24  24  18  22  20  10                  200 Reading    62  66  52  58  60  50  58  82  48  26  84  42                  100 Reading    36  38  32  32  34  30  36  50  30  22  52  28                  6 Reading      4   6   6   6   8   6   10  14  12  24  18  16                  3 Reading      6   4   5   4   6   5   8   12  10  22  16  15                  Gel Strength (10 sec)                                                                         6   6   8   8   10  8   14  18  16  24  18  18                  Gel Strength (10 min)                                                                         6   8   14  10  18  14  16  32  26  34  40  32                  __________________________________________________________________________      *0.5 ppb SPACER SPERSE.                                                        **1.0 ppb SPACER SPERSE.                                                 

                                      TABLE 3                                      __________________________________________________________________________                        Weight, Pounds Per Gallon                                                      16.5                                                                               17.0                                                                               17.6                                                                               16.5                                                                               17.0                                                                               17.6                                    __________________________________________________________________________     Fresh Water (gal)  22.58                                                                              21.92                                                                              20.64                                                                              22.72                                                                              21.96                                                                              20.64                                   Sulfonate Dispersant (ppb)                                                                        0.2 0.2 0.2 0.2 0.2 0.2                                     Weighting Agent (ppb)                                                                             251 243 231 251 243 231                                     Oleyl Amide Dispersant (ppb)                                                                      1.5 2.0 3.0 1.5 2.0 3.0                                     Weighting Agent, Iron Carbonate (ppb)                                                             254 285 334 254 285 334                                     Viscosifier, HEC (ppb)                                                                            3.0 3.0 2.5 3.0 3.0 2.5                                     Inhibitor, KCl (ppb)                                                                              10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                                               10.5                                                       Initial Rheology                                                                              Initial Rheology                                                at 72° F                                                                               at 150° F                             Apparent Viscosity  300+                                                                                300+                                                                                300+                                                                               165                                                                               171                                                                               200                                    600 Reading         600+                                                                                600+                                                                                600+                                                                               330                                                                               342                                                                               400                                    300 Reading         600+                                                                                600+                                                                                600+                                                                               230                                                                               219                                                                               230                                    Plastic Viscosity  --   --   --   100                                                                               123                                                                               170                                    Yield Point        --   --   --   130                                                                                96                                                                                60                                    200 Reading        474  520  599  208                                                                               166                                                                               168                                    100 Reading        306  336  370  160                                                                               114                                                                               102                                    6 Reading           78    80  68   36                                                                                44                                                                                24                                    3 Reading           62   64   52   32                                                                                40                                                                                24                                    Gel Strength (10 sec)                                                                              70   72  130   38                                                                                50                                                                                66                                    Gel Strength (10 min)                                                                             140  130  250   74                                                                                88                                                                               134                                    pH                 8.5  8.5  8.5  -- -- --                                     API Fluid Loss (mls/30 min)                                                                       5.0  5.5  4.9  -- -- --                                     HT-HP Fluid Loss - 450 psi 250° F                                                          3.0  24*   34  -- -- --                                     __________________________________________________________________________      *Fluid loss at 220° F.                                            

                                      TABLE 4                                      __________________________________________________________________________     17 ppg HYDROWATE                                                                       21.96 gal. Water                                                               0.2 ppb Sulfonate Dispersant                                                   2.0 ppb Oleyl Amide Dispersant                                                 248 ppb CaCO.sub.3 Weighting Agent                                             285 ppb Iron Carbonate Weighting Agent                                           ppb HEC Variable Viscosifier                                                 10.5 ppb KCl Inhibitor                                                 Viscosifier     2.0           3.0                                              Temperature ° F                                                                         72   150                                                                               175                                                                               200                                                                               72   150                                         __________________________________________________________________________     Apparent Viscosity                                                                              300+                                                                               150                                                                               110                                                                               81  300+                                                                               171                                         600 Reading      600+                                                                               300                                                                               220                                                                               162                                                                                600+                                                                               342                                         300 Reading     548  176                                                                               138                                                                               104                                                                                600+                                                                               219                                         Plastic Viscosity                                                                              --   124                                                                               82 58 --   123                                         Yield Point     --   52 56 46 --    96                                         200 Reading     442  134                                                                               104                                                                               82 520  166                                         100 Reading     270  84 68 56 336  114                                         6 Reading        62  26 22 20  80   44                                         3 Reading        52  21 20 18  64   40                                         Gel Strength (10 sec.)                                                                          66  32 -- --  72   50                                         Gel Strength (10 min.)                                                                         118  66 -- -- 130   88                                         API Fluid Loss (mls/30 min)                                                                    8.6  -- -- -- 5.5  --                                          HT-HP Fluid Loss (mls/30 min.)                                                 150° F    30  -- -- -- 16.8 --                                          220° F   --   -- -- --  24  --                                          __________________________________________________________________________

                                      TABLE 5                                      __________________________________________________________________________     Variation of Rheology With pH                                                  Initial Rheology of 14 ppg HYDROWATE Fluid at 72° F                                    pH                                                                             6.1                                                                               7.05                                                                              8.05                                                                              8.65                                                                              9.4                                                                               9.75                                                                              10.75                                                                             11.25                                                                             12.0                                    __________________________________________________________________________     Apparent Viscosity                                                                            201                                                                               222                                                                               275                                                                               280                                                                               271                                                                               270                                                                               253                                                                               255                                                                               242                                     600 Reading    402                                                                               444                                                                               550                                                                               560                                                                               542                                                                               540                                                                               506                                                                               510                                                                               484                                     300 Reading    238                                                                               264                                                                               326                                                                               334                                                                               322                                                                               320                                                                               300                                                                               301                                                                               286                                     Plastic Viscosity                                                                             164                                                                               180                                                                               224                                                                               226                                                                               220                                                                               220                                                                               206                                                                               209                                                                               198                                     Yield Point     74                                                                                84                                                                               102                                                                               108                                                                               102                                                                               100                                                                                94                                                                                92                                                                                88                                     200 Reading    174                                                                               192                                                                               238                                                                               246                                                                               236                                                                               224                                                                               220                                                                               220                                                                               208                                     100 Reading    100                                                                               110                                                                               138                                                                               142                                                                               136                                                                               134                                                                               126                                                                               126                                                                               120                                     6 Reading       11                                                                                12                                                                                18                                                                                18                                                                                16                                                                                16                                                                                15                                                                                16                                                                                15                                     3 Reading       7  8  12                                                                                12                                                                                10                                                                                12                                                                                10                                                                                10                                                                                10                                     Gel Strength (10 sec.)                                                                         8  10                                                                                14                                                                                16                                                                                14                                                                                16                                                                                14                                                                                14                                                                                14                                     Gel Strength (10 min.)                                                                         14                                                                                14                                                                                22                                                                                22                                                                                19                                                                                24                                                                                20                                                                                20                                                                                20                                     API Fluid Loss (mls/30 min.)                                                                  5.7                                                                               5.4                                                                               4.4                                                                               4.6                                                                               4.8                                                                               3.8                                                                               4.3                                                                               4.6                                                                               4.4                                     __________________________________________________________________________

                                      TABLE 6                                      __________________________________________________________________________             One Barrel - 17 ppg                                                            HYDROWATE Aging Test                                                           Water                   21.96                                                                             gal.                                                Sulfonate Dispersant    0.20                                                                              ppb                                                 CaCO.sub.3 Weighting Agent                                                                             245                                                                               ppb                                                 Oleyl Amide Dispersant  2.0                                                                               ppb                                                 Iron Carbonate Weighting Agent                                                                         285                                                                               ppb                                                 HEC Viscosifier         3.0                                                                               ppb                                                 KCl Inhibitor           10.5                                                                              ppb                                                       First Day Third Day                                                            Left Right                                                                               Left       Right                                       Turbo Blender Tank                                                                           Tank Tank Tank       Tank                                        Temperature ° F                                                                       72   72   72   150                                                                               175                                                                               72   150                                                                               175                                 __________________________________________________________________________     Apparent Viscosity (UV)                                                                       300+                                                                                300+                                                                                300+                                                                               185                                                                               147                                                                                300+                                                                               179                                                                               147                                 600 Reading    600+                                                                                600+                                                                                600+                                                                               370                                                                               294                                                                                600+                                                                               358                                                                               294                                 300 Reading   462  500  560  246                                                                               206                                                                               580  238                                                                               194                                 Plastic Viscosity (UV)                                                                       --   --   --   124                                                                                88                                                                               --   120                                                                               100                                 Yield Point (lbs/100 sq.ft.)                                                                 --   --   --   122                                                                               118                                                                               --   118                                                                                94                                 200 Reading   360  390  434  200                                                                               170                                                                               454  188                                                                               154                                 100 Reading   240  258  284  144                                                                               136                                                                               296  130                                                                               110                                 6 Reading      70   68   70   64                                                                                62                                                                                76   52                                                                                50                                 3 Reading      58   58   58   58                                                                                58                                                                                60   48                                                                                42                                 Gel Strength (10 sec.)                                                         (lbs/100 sq. ft.)                                                                            --   --   --    60                                                                               -- --    50                                                                               --                                  Gel Strength (10 min.)                                                         (lbs/100 sq. ft.)                                                                            --   --   --    76                                                                               -- --    72                                                                               --                                  API Fluid Loss (mls/30 min)                                                                  --   --    5.4 -- --  5.3 -- --                                  HT-HP Fluid Loss (250° F -                                              450 psi) (mls/30 min)                                                                        --   --   19.0 -- -- 18.8 -- --                                  Weight (ppg)  17.0 17.0 17.0 -- -- 17.0 -- --                                  __________________________________________________________________________      NOTE:                                                                          In the make-up, the oleyl amide dispersant was added along with the iron       carbonate to eliminate foaming.                                                UV = Unit Viscosity                                                      

                  TABLE 6                                                          ______________________________________                                         Fluid                                                                          No.    Description                                                             ______________________________________                                         A      HYDROWATE (17.0 ppg) aged 18 days.                                      B      HYDROWATE contained in storage tank as mixed on                                16th day.                                                               C      Combination of Fluid A and B after 19th day.                            Fluid No.       *A        B         C                                          Temperature ° F                                                                         72        72        72                                         ______________________________________                                         Apparent Viscosity (UV)                                                                         300+      300+      300+                                      600 Reading      600+      600+      600+                                      30 Reading      526        600+     510                                        Plastic Viscosity (UV)                                                                         --        --        --                                         Yield Point (lbs/100 sq. ft.)                                                                  --        --        --                                         200 Reading     416       500       400                                        100 Reading     280       316       270                                        6 Reading        78        60        86                                        3 Reading        70        24        72                                        Weight (ppg)     17.0      16.8      17.0                                      ______________________________________                                          *Fluid A had set static in storage tanks for 20 days. The fluid was            stirred one time during the 20 days. There was no settling of solids and       no change in properties.                                                 

                  TABLE 7                                                          ______________________________________                                         HYDROWATE Completion Fluid Formula: Core Tests                                 Density - 15.0 ppg                                                             One Barrel Make-Up                                                             ______________________________________                                         Fresh Water            22.2   gal.                                             Sulfonate Dispersant   0.5    ppb                                              CaCO.sub.3 Weighting Agent                                                                            445    ppb                                              HEC Viscosifier        2.0    ppb                                              KCl Inhibitor          10.5   ppb                                              ______________________________________                                    

Test A

Step 1 -- Morrow crude flowed through Berea core. Flow Rate = 100 cc/10 min. (10 cc/min.) at 100 psi and 150° F.

Step 2 -- Core backflowed with HYDROWATE completion fluid. Flow Rate = 21/2 cc/10 min. (0.25 cc/min.)

Step 3 -- Morrow crude flowed through Berea core same direction as Step 1. Flow Rate = 100 cc/9 min. (11.1 cc/min.).

Test B

Step 1 -- Morrow crude flowed through Berea core. Flow Rate = 198 cc/17 min. (11.65 cc/min.)

Step 2 -- Core backflowed with HYDROWATE completion fluid. Flow Rate = 1 cc/30 min.

Step 3 -- Core lightly rinsed with water to remove all fluid except filter cake. 15% HCl acid was allowed to remain static on cake for 20 min. Next, the 15% HCl acid was flowed through core in same direction as Step 2. Flow rate = 218 cc/13 min. (16.77 cc/min.).

Step 4 -- Morrow crude was flowed through Berea core in same direction as Step 1. Flow Rate = 199 cc/61/2 min. (30.6 cc/min.).

Test C

Step 1 -- Morrow crude flowed through Berea core. Flow Rate = 157 cc/30 min. (5.23 cc/min.)

Step 2 -- Core backflowed using 15% HCl. Flow rate = 213 cc/2 min. (106.5 cc/min.).

Step 3 -- Core flowed with Morrow crude through in same direction as Step 1. Flow Rate = 207 cc/151/2 min. (13.35 cc/min.)

HYDROWATE fluid was mixed on a Hamilton Beach Mixer with Dayton 5 amp rheostat set on 10. The mixing procedure was as follows:

1. Measure out required amount of water.

2. While mixing, add required amount of dispersant then continue mixing one minute.

3. While mixing, slowly add required amount of weighting agent, then continue mixing two minutes.

4. While mixing, slowly add required amount of viscosifier and continue mixing 10 minutes.

5. While mixing, slowly add required amount of inhibitor and continue mixing three minutes.

A No. 2 spring was used in the Model 35 Fann VG Meter for recording the rheological properties and all the readings taken were doubled.

                                      TABLE 8                                      __________________________________________________________________________     13.0 ppg HYDROWATE Aqueous Fluid                                                         Fresh Water            28.1                                                                              gal.                                                 CaCO.sub.3 Weighting Agent                                                                            312                                                                               ppb                                                  HEC Viscosifier        3.0                                                                               ppb                                                  KCl Inhibitor          10.5                                                                              ppb                                        Sulfonate Dispersant (ppb)                                                                        0      0.1    0.2    0.3                                    Temperature ° F                                                                            72  160                                                                               72  160                                                                               72  160                                                                               72  160                                __________________________________________________________________________     Apparent Viscosity 110 50 94  44 99  37 87  33                                 600 Reading        220 100                                                                               188 88 198 74 174 66                                 300 Reading        135 66 110 54 114 44 97  37                                 Plastic Viscosity  85  34 78  34 84  30 77  29                                 Yield Point        50  32 32  20 30  14 20   8                                 200 Reading        100 54 80  42 82  32 68  27                                 100 Reading        60  39 46  28 48  20 37  16                                 6 Reading          12  14 7    9 6    6 4    4                                 3 Reading          9   13 5    8 4    4 3    3                                 Gel Strength (10 sec.)                                                                            10  18 6    9 6    6 4    5                                 Gel Strength (10 min.)                                                                            17  25 10  16 16  14 7    8                                 API Fluid Loss (mls/30 min.)                                                                      6.8 -- 5.4 -- 4.9 -- 6.2 --                                 13.0 ppg                                                                                 Fresh Water            28.1                                                                              gal.                                                 Sulfonate Dispersant   0.2                                                                               ppb                                                  CaCO.sub.3 Weighting Agent                                                                            312                                                                               ppb                                                  KCl Inhibitor          10.5                                                                              ppb                                        HEC Viscosifier                                                                               2.0   3.0    3.5    4.0    4.5                                  Temperature ° F                                                                        72 160                                                                               72  160                                                                               72  160                                                                               72  160                                                                               72  160                              __________________________________________________________________________     Apparent Viscosity                                                                            46.5                                                                              24 99  37 133 53 186 69 224 80                               600 Reading    93 48 198 74 266 106                                                                               372 138                                                                               448 160                              300 Reading    51 30 114 44 156 62 230 80 270 94                               Plastic Viscosity                                                                             42 18 84  30 110 44 142 58 178 66                               Yield Point    9  12 30  14 46  18 88  22 92  28                               200 Reading    36 24 82  32 114 46 170 60 202 70                               100 Reading    20 16 48  20 64  28 100 34 120 40                               6 Reading      3   6 6    6 8    6 12   8 14   8                               3 Reading      2    5                                                                               4    4 6    5 8    6 10   7                               Gel Strength (10 sec.)                                                                        3   8 6    6 8    8 10  10 12  10                               Gel Strength (10 min.)                                                                        7  13 16  14 16  16 16  18 20  17                               API Fluid Loss (mls/30 min.)                                                                  7.1                                                                               -- 4.9 -- 4.9 -- 4.7 -- 4.3 --                               __________________________________________________________________________

                                      TABLE 9                                      __________________________________________________________________________     16.0 ppg                                                                                 Water                 19.2                                                                              gal.                                                  Sulfonate Dispersant  1.0                                                                               ppb                                                   CaCO.sub.3 Weighting Agent                                                                           512                                                                               ppb                                                   HEC Viscosifier       0.5                                                                               ppb                                                   KCl Inhibitor         10.5                                                                              ppb                                         Sulfonate Dispersant (ppb)                                                                    0.5     1.0     2.0     2.5                                     Temperature ° F                                                                        72   160                                                                               72   160                                                                               72   160                                                                               72   160                                __________________________________________________________________________     Apparent Viscosity                                                                             300+                                                                               117                                                                                300+                                                                               105                                                                                300+                                                                               102                                                                                300+                                                                               93                                 600 Reading     600+                                                                               234                                                                                600+                                                                               210                                                                                600+                                                                               204                                                                                600+                                                                               186                                300 Reading    430  114                                                                               300  114                                                                               302  110                                                                               306  100                                Plastic Viscosity                                                                             --   94 --   96 --   94 --   86                                 Yield Point    --   46 --   18 --   16 --   14                                 200 Reading    306  96 190  80 200  76 198  70                                 100 Reading    168  60  92  50 100  44  98  40                                 6 Reading       36  20  18  16  16  14  16  14                                 3 Reading       30  18  14  15  12  13  12  12                                 Gel Strength (10 sec.)                                                                         19  20  18  18  16  18  16  16                                 Gel Strength (10 min.)                                                                         40  34  30  38  30  32  32  24                                 API Fluid Loss (mls/30 min.)                                                                   11.8                                                                               --  10.4                                                                               --  7.6 --  7.0 --                                           Water                 19.2                                                                              gal.                                                  Sulfonate Dispersant  2.5                                                                               ppb                                                   CaCO.sub.3 Weighting Agent                                                                           512                                                                               ppb                                                   HEC Viscosifier       0.5                                                                               ppb                                                   KCl Inhibitor         10.2                                                                              ppb                                         Sulfonate Dispersant (ppb)                                                                          0          1.5      2.0                                   Temperature ° F                                                                              72   160   72 160   72 160                                __________________________________________________________________________     Apparent Viscosity    300+                                                                               120   214                                                                               72    212                                                                               61                                 600 Reading           600+                                                                               240   428                                                                               144   424                                                                               122                                300 Reading           600+                                                                               140   212                                                                               76    202                                                                               68                                 Plastic Viscosity    --   100   216                                                                               68    222                                                                               54                                 Yield Point          --   40    --  8    -- 14                                 200 Reading           600+                                                                               106   136                                                                               54    126                                                                               44                                 100 Reading          422  72    68 36     58                                                                               25                                 6 Reading             70  30    20 18     8  7                                 3 Reading             48  22    18 16     6  6                                 Gel Strength (10 sec.)                                                                              102  26    28 18     8  9                                 Gel Strength (10 min.)                                                                              142  54    38 34     12                                                                               14                                 API Fluid Loss (mls/30 min.)                                                                        NC*  --     5.8                                                                              --     5.9                                                                              --                                           Water                 19.2                                                                              gal.                                                  Sulfonate Dispersant  2.5                                                                               ppb                                                   Oleyl Amide Dispersant                                                                               1.0                                                                               ppb                                                   CaCO.sub.3 Weighting Agent                                                                           512                                                                               ppb                                                   KCl Inhibitor         10.5                                                                              ppb                                         HEC Viscosifier (ppb)                                                                          0.3    0.4    0.5      0.6                                     Temperature ° F                                                                         72 160 72 160 72   160 72   160                                __________________________________________________________________________     Apparent Viscosity                                                                             237                                                                               85  215                                                                               85   300+                                                                               93   300+                                                                               93                                 600 Reading     474                                                                               170 430                                                                               170  600+                                                                               186  600+                                                                               186                                300 Reading     230                                                                               90  220                                                                               92  306  100 376  104                                Plastic Viscosity                                                                              244                                                                               80  210                                                                               78  --   86  --   82                                 Yield Point      0 10   10                                                                               14  --   14  --   22                                 200 Reading     152                                                                               64  150                                                                               64  198  70  254  74                                 100 Reading      76                                                                               38   76                                                                               38   98  40  140  48                                 6 Reading        14                                                                               14   12                                                                               14   16  14   36  20                                 3 Reading        10                                                                               12   10                                                                               12   12  12   30  18                                 Gel Strength (10 sec.)                                                                          8 17   14                                                                               16   16  16   34  20                                 Gel Strength (10 min.)                                                                          36                                                                               42   34                                                                               38   32  24   54  16                                 API Fluid Loss (mls/30 min.)                                                                    9.0                                                                              --   9.4                                                                              --   7.0 --   5.4 --                                 __________________________________________________________________________      *No Control                                                              

                  TABLE 10                                                         ______________________________________                                         Viscosities of HEC Polymers                                                    Limits of Viscosity of Aqueous Solutions                                                  Brookfield Viscosity at 25° C, cps                           Polymer    at Varying Concentrations                                           Type       1%          2%          5%                                          ______________________________________                                         HH         3,400-5,000 --          --                                          H4         2,600-3,300 --          --                                          H          1,500-2,500 --          --                                          MH         1,000-1,500 --          --                                          M          --          4,500-6,500 --                                          K          --          1,500-2,500 --                                          G          --          150-400     --                                          E          --           25-105     --                                          J          --          --          150-400                                     L          --          --           75-150                                     ______________________________________                                     

I claim:
 1. A high stability nondamaging fluid for maintaining a hydrostatic pressure on a subterranean formation intersected by a well comprising water, a viscosifier which is present in an effective concentration to suspend weighting agent, said viscosifier being selected from a hydratable hydroxy alkyl substituted cellulose polymer wherein the hydroxy alkyl substituents have 2-3 carbon atoms; an inhibitor which is present in an effective concentration to inhibit clay swelling comprising at least one water soluble halide salt of alkali metal, alkaline earth metal or ammonium; a water insoluble, relatively inert finely divided particulate solid weighting agent having a mean particle size in the range of about 2-20 microns, said weighting agent being present in a concentration to give the desired fluid density; and a dispersant having a concentration of less than about 1.5% by weight of said fluid, said dispersant comprising at least one or a combination of a condensation product of naphthalene sulfonate and formaldehyde or a fatty acid amide-lignin liquor mixture, wherein the fatty acid precursor contains about 14-18 carbon atoms, the amine precursor is a low molecular weight amino sulfonic acid having 1-6 carbon atoms and the lignin is sulfonated.
 2. A high stability, nondamaging fluid of claim 1 in which the viscosifier is selected from hydroxyethylcellulose polymers having a viscosity in water at a concentration of 1% or less than about 5,000 cp.
 3. A high stability, nondamaging fluid of claim 1 in which the inhibitor is a chloride salt of an alkali metal.
 4. A high stability, nondamaging fluid of claim 1 having a density greater than about 13.6 ppg.
 5. A high stability, nondamaging fluid of claim 1 having a density greater than about 16.0 ppg.
 6. A high stability, high density fluid of claim 1 having a density of 13 pounds per gallon or higher in which the weighting agent is iron carbonate, calcium carbonate or a combination thereof.
 7. A high stability, high density fluid of claim 6 in which the inhibitor is a chloride, bromide or combination thereof with sodium, potassium, magnesium or calcium or a combination thereof.
 8. A high stability nondamaging fluid for maintaining a hydrostatic pressure on a subterranean formation intersected by a well comprising water; a viscosifier which is present in an effective concentration to suspend weighting agent up to about 0.1% by weight of said fluid, said viscosifier being selected from a hydratable hydroxy alkyl cellulose polymer wherein the the hydroxy alkyl group has 2-3 carbon atoms; an inhibitor which is present in an effective concentration to inhibit clay swelling up to about 15% by weight of said fluid comprising at least one water soluble halide salt of alkali metal, alkaline earth metal or ammonium in which the halide is bromide or chloride; a water insoluble, acid soluble finely divided particulate solid weighting agent having a specific gravity of at least 2.0 and a mean particle size in the range of about 2-20 microns, said weighting agent comprising at least one or a combination of calcium carbonate or iron carbonate and being present in a concentration to give the desired fluid density; and a dispersant having a concentration of less than about 1.5% by weight of said fluid, said dispersant comprising at least one or a combination of condensation product of naphthalene sulfonate and formaldehyde or a fatty acid amide-lignin liquor mixture, wherein the fatty acid precursor contains about 14-18 carbon atoms, the amine precursor is a low molecular weight amino sulfonic acid having 1-6 carbon atoms and the lignin is sulfonated.
 9. A fluid of claim 8 wherein the viscosifier is a hydroxyethylcellulose polymer, the fluid has a density greater than about 13.6 ppg and the fatty acid is oleic acid.
 10. A fluid of claim 9 wherein the sulfonic acid contains about 3 carbon atoms.
 11. A method of controlling the hydrostatic pressure in a well adjacent a subterranean formation without damaging said formation comprising placing in said well a fluid having a density sufficient to maintain a hydrostatic pressure on said formation which is higher than the pressure exerted by the fluid in said formation, said fluid comprising water; a viscosifier which is present in an effective concentration to suspend weighting agent, said viscosifier being selected from a hydratable hydroxy alkyl cellulose polymer wherein the hydroxy alkyl substituents have 2-3 carbon atoms; an inhibitor which is present in an effective concentration to inhibit clay swelling comprising at least one water soluble halide salt of alkali metal, alkaline earth metal or ammonium; a relatively inert water insoluble finely divided particulate weighting agent having a mean particle size in the range of about 2-20 microns, said weighting agent being present in a concentration to give the desired fluid density; and a dispersant comprising at least one or a combination of a condensation product of naphthalene sulfonate and formaldehyde or a fatty acid amide-lignin liquor mixture, wherein the fatty acid precursor contains about 14-18 carbon atoms, the amine precursor is a low molecular weight amino sulfonic acid having 1-6 carbon atoms and the lignin is sulfonated. 